Section 22. (a) Whoever has sexual intercourse or unnatural sexual intercourse with a person, and compels such person to submit by force and against his will, or compels such person to submit by threat of bodily injury and if either such sexual intercourse or unnatural sexual intercourse results in or is committed with acts resulting in serious bodily injury, or is committed by a joint enterprise, or is committed during the commission or attempted commission of an offense defined in section fifteen A, fifteen B, seventeen, nineteen or twenty-six of this chapter, section fourteen, fifteen, sixteen, seventeen or eighteen of chapter two hundred and sixty-six or section ten of chapter two hundred and sixty-nine shall be punished by imprisonment in the state prison for life or for any term of years.

No person serving a sentence for a second or subsequent such offense shall be eligible for furlough, temporary release, or education, training or employment programs established outside a correctional facility until such person shall have served two-thirds of such minimum sentence or if such person has two or more sentences to be served otherwise than concurrently, two-thirds of the aggregate of the minimum terms of such several sentences.

(b) Whoever has sexual intercourse or unnatural sexual intercourse with a person and compels such person to submit by force and against his will, or compels such person to submit by threat of bodily injury, shall be punished by imprisonment in the state prison for not more than twenty years; and whoever commits a second or subsequent such offense shall be punished by imprisonment in the state prison for life or for any term or years.

Whoever commits any offense described in this section while being armed with a firearm, rifle, shotgun, machine-gun or assault weapon, shall be punished by imprisonment in the state prison for not less than ten years. Whoever commits a second or subsequent such offense shall be punished by imprisonment in the state prison for life or for any term of years, but not less than 15 years.

No person serving a sentence for a second or subsequent such offense shall be eligible for furlough, temporary release, or education, training or employment programs established outside a correctional facility until such person shall have served two-thirds of such minimum sentence or if such person has two or more sentences to be served otherwise than concurrently, two-thirds of the aggregate of the minimum terms of such several sentences.

For the purposes of prosecution, the offense described in subsection (b) shall be a lesser included offense to that described in subsection (a).